1. Field of the Invention
This invention relates to a method of producing fine and uniform bismuth titanate powders or particles used for electronic components such as capacitors.
2. Description of the Prior Art
Recently, the methods of producing comminuted ferroelectric materials have been studied from many aspects. There comminuted ferroelectric materials are used e.g. for ceramic capacitors. In association with the demand for reduced size and increased packing density of electronic parts, it has been desired to reduce the size and weight while increasing the capacity and high frequency characteristics of the ceramic capacitors. To this end, it is necessary to reduce the size of the ferroelectric material in order to make the ceramic layer thin and uniform.
On the other hand, in order to improve calcination and temperature characteristics of the ceramic capacitors, it is necessary to elevate the heat treatment temperature. However on such occasion, the resulting capacitor may not be of uniform properties because of vaporization of the lead oxide PbO contained in the starting material. Therefore it becomes necessary to lower the calcination temperature to present vaporization of lead oxide PbO. Thus, fine powders of the ferroelectric materials are desired in order to make the properties of the ceramic capacitors more uniform.
When the ferroelectric materials are used as starting materials for preparing electrostrictive, piezoelectric on transparent ceramic material, other than the capacitor material, the ferroelectric materials of the small and uniform particle size are sequired in order to improve calcinerability or temperature characteristics.
These ferroelectric materials include bismuth titanate Bi.sub.4 (TiO.sub.4).sub.3 endowed with various properties. The Bi.sub.4 (TiO.sub.4).sub.3 particles are usually prepared by that bismuth carbonate Bi.sub.2 (CO.sub.3)O.sub.2.0.5H.sub.2 O or Bi.sub.2 O.sub.3 and titanium oxide TiO.sub.2 are ball-milled and subjected to a solid phase reaction at an elevated temperature of 600.degree. to 900.degree. C. to be again ball-milled to fine particle size and passed through a sieve.
These bismuth titanate fine particles are however inconvenient because of rather poor particle size distribution of the ball milled material, and possible inclusion of coarse size particle or impurity metal oxide due to prolonged crushing.